Classification system for pulverized materials



H. HARDINGE CLASSIFICATION SYSTEM FOR PULVERIZED MATERIALS Filed Nov. 121936 2 Sheets-Sheet 1 Oct. 3, 1939. H. HARDINGE.

CLASSIFICATION SYSTEM FOR PULVERIZED MATERIALS I Filed Nov. '12, 1936 rmm HARLOWE HARDING-E M MW. W

- Patented Oct. 3, 1939'- UNITED STATES almost cmssmcsnon srsnm ron.

. PULVERIZED m'ramns Barlowe Hardinge, York, Pa. asslgnor to HardinOompa Incorporated, York, Pa., a corporation of ew York ApplicationNovember 12, 1930, Serial No. 110,429 3 Claims. (01. 83-3) Thisinvention relates to grinding mills and pulverizers, and moreparticularly to a system for classifying the material pulverized in themills or pulverizers.

, object of. the invention is to provide'an improved pulverizingapparatus in which the feed, oversize, and air all enter and leave atthe same end of the apparatus. i

Another object of the invention is to provide an improved pulverizingapparatus in which the material is fed to a grinding mill in such 'amanner that it mingles with the dry oversize material discharged from aclassifier prior to coming in contact with dry air being conducted tothe mill,

'16 so that the wet feed is partially ,dried, thereby enabling the freshdry air which subsequently contacts the feed to quickly remove orabsorbmoisture in the feed before the feed enters the mill.

- With the foregoing and other-objects and advantages in view, theinvention consists in the preferred construction and arrangement of theseveral parts which willbe hereinafter fully described and claimed.

25 In the accompanying, drawings:

Figure 1 is a general view, partly in vertical section, and partly inelevation, showing one form of the invention in connection with acylindrical ball mill; and

30 Fig. 2 is a view, similar to Fig. 1, of another form of the inventionin connection with a conical mill.

Referring'to the drawings and especially to Fig. 1, the materialpulverizing. and collecting system may be characterized as aclosed-circuit system in which fluid currents, such as air, arecirculated throughout the system. It includes a pulverizing mill H,which may be of any 'wellknown construction having hollow trunnions I 2,

40 II, at each end, the trunnion I 2 in the instant case being closed bya plate or cover ll, so that only the trunnion l3 at the other end ofthe mill is open.

' The air or other elastic fluid whicli conveys 4 the fine product iscaused to circulate continuously through the system by a blower II,which discharges directly'into the open end I: of the mill ll throughfixed conduit 16 and rotating conduit I'I. I v

5o Conduit I1 is mounted in the discharge hollow trunnion II, beingspaced a suitable distance from the interior of said trunnion, so as toprm .vide an annular space II for the dust andfiuid leaving the mill ll.

The inner end of conduit l1 pr jects into the mill II a suitabledistance, and a grate l9 extends from the inner portion of said conduitoutwardly to a conical ball rejector 20 extending inwardly from the endwall of the mill ll.

Extending from the wall of the ball rejector 5 20 to the conduit l1 andlocated on the outer side of the grate I 9, are lifters 2|, the purposeof which will be hereinafter described.

It is usual to'feed material into .pulverizing millsautomatically. Thematerial descends from 1 a bin into a hopper 22 and is permitted to passinto chute 22 by means of a rotary pocket feeder 24.

Feeders of this type are known as an air-lock type of feeder and suchfeeders are adapted toprevent positive pressure from being carriedupwardly into the hopper 22. However, it will be understood that anytype of. feeder which would choke off the air from entering the hopperwill be satisfactory. 'Ihe feed from chute 23 passes in-and around 7 thebottom of a classifier "and enters conduit 28.- In passing through theclassifier 25, the

feed joins with the oversize dropped from the classifier. This helps todry the wet feed, as the 25 oversize is very dry. and mingling with thefeed, picks. up any free moisture and-has the advantage of absorbingthis moisture over a large surface area so that the air also enteringthe mill II will evaporate this 'moisture more rapidly than if the feedwere placed in contact with the air without first mingling with the'oversize.

Below theconduit 28 is a movable gate 21, which is provided to preventback pressure of air from entering the lower portion of the classifier25 before it should. The gate 21 is so balanced that pressure of theoversize and the feed on top of it, overcomes the back pressure of airbelow, and the oversize and feed trickle down past the gate into conduit28, and from thence enter the 40 conduit l-l near the inner end of saidconduit 16.

The blower l5 draws air in the suction conduit 29 from an outsidesource, and if appreciable moisture is present, it is preferable toprovide means for supplying hot air through conduit 29, as this hot airwill dry the moisture in the feed more rapidly than cold air, as is wellknown in the art. The hot air then travels through conduit l6 and mixeswith the feed and oversize entering conduit it from the feedconduit .28and conveys the feed and oversize by forced draft through the rotatingconduit ll into the mill ll. e

As shown by the arrows,;1"lg. 1, the air after entering. the mill Hreverses and-flows outwardly through the grate "and into the annularspace I8 between conduit l1 and trunnion l3. The ball rejector 20,heretofore referred to, forms a pocket. and the lifters 2| pick up anytramp oversize, small balls and refuse which may" lodge between thegrate l3 and the ball rejector 20. The oversize then slides down thelifters 2| as they rotate with the mill II and enters the conduit Hwhere the air forces the oversize back into the mill l I.

The air circulating through the mill ll picks up the-fine product in theform of dust, and carries this dust outwardly through the grate I 3, andannular space I8, and conduit 30, to classifler 25. I The classifier 25has an inner casing 3| along the outside of which flows the current ofmaterlal-laden air entering through conduit 30. The vortex createdwithin the classifier causes the heavier particles to be cast outof thestream of flowing air. These heavy or'large' particles leave the innercasing 3i at its lower end 32,

which directs such particles towardsthe fresh feed inconduit 25, and asstated before, helps'to dry the incoming feed. Oversize also drops outaround the casing of the classifier 25 and in sliding down the sides,also mingles with the incom- The fines then pass through conduit 33 intoa burner 34,- if the operation is one using the conventional form ofwhat is known as a unit pulverizer fordirect firing of powered fuel.

7 It will be noted that the blower l places the while systemunder'pressure; with a mill under pressure, loss of air would be likelyto occur at the joint 35 between the inner end of the nonrotating'conduit 30, andthe outer end of the rotating trunnion II of the mill ll,if no provision-were made to prevent such occurrence. Therefore, Ienclose the. joint "with a box- 31, which forms a Joint with theflangeorouter end 38 of the trunnion l3. This Joint is made to' "fit asclosely as is practicable by methods ordinarily used.

Connected to the'chamber under sufficient pressure into the joint'toprevent the escape of. dirty air and oversize from the apparatus at thisjoint.

In order to control the operation of the device, there is a damper 40which regulates the amount of incoming air from the Blower l5;

entering the mill II. V

There is also a damper 4| which regulates the same air, but in this casebypasses the air around the mill H directly to the classifier 25,through conduit 42 which connects conduit IS with conduit 30.

When during operation the capacity is reduced below the rated output ofthe apparatus by partially closing damper 40-, the yelocity in thesystem, particularly in the classifier 25 and conduit 33, may be belowthe velocity which is suflicient to carry all of the material insuspension.

' current of air is reversed and in passing through her GI, from whenceit passes from'the classifier .through conduit 62.

. within box :1 by pipe 39, is a small blower 35, which forces-air I thefeeder 38 is located above conduit 69, at its the one hand and a pulleffect on the other.

-the There method .ofoperation, not only because the comis a distinctadvantage in this bination of thefeed mixing with the oversize and theair, dries the feed, thereby increasing the grinding capacity of themill, but the whole unit is simple inoonstruction, and there isconsiderable saving in floor space over the conven tional form ofpulverizing unit, where there are apparatus at both ends of the mill.

Referringnow to the form of the invention shown in Fig. .2, the air orother elastic fluid which conveys the fine'product'is caused tocirculate continuously through the system by blower 5|, which dischargesdirectly into the hollow trunnion end 52 of a pulverizing conical type-of mill 53, through conduits 54 and 55.

The hollow trunnion end of the mill 53, opposite to the trunnion 52 isclosed by a cover plate 56, so that within the mill the direction of thethe mill the current of air picks up fine particles which are desired tobe collected.

The air,laden with material, passes through grate 51 and leaves the millthrough annular space 58 between conduit 55 and trunnion 52.

Lifters 59 pick up anytramp oversize, small balls and refuse, and suchmaterial slides down the lifters asthey rotate with the mill 53 andenters the conduit 55 where the air forces the oversize back into themill 53.

Y The air, laden with material, which leaves the knill through the space58, passes through conduit 50 and enters the outer chamber of classi-Conduit 62 is vci'mnectedwith a cyclone dust collector 63 in which thematerial is relieved fromthe air by- ;the action taking place within thecollector. 1

The air is drawn from the collector 63 through conduit 64- by means ofblower 5|, whose suction side isconnected with conduit 64.

When the material-laden air enters the outer chamber of the classifier6i, its velocity is lessened and its carrying capacity is reduced, withthe result thematerial of undesired coarseness drops to the lowerportion of the inner cone 61 of the classifier. k

In the form of the invention shown in Fig. 2,

lower end with the. inner end portion of conduit 54.

The lower portion of the classifier 5| is connected to conduit 69 by aconduit 10, and the lower portion of the inner cone 51 of the classifierhas a depending chute 1|, which directs the oversize towards conduitBelow the point in conduit 59 at which the con- I duit Ill is connected,there is a gate 12, similar in function to the gate 21 heretoforedescribed.

In this form of the invention, there will be no back pressure at thepoint wltifre the oversize enters the mill, as there may e very nearly aneutral pressure, or perhaps a suction, if the mill is operating inbalance. This balanced operation is obtained by the blower 5| forcingthe air through conduit 54 into the mill 53, and also sucking in airthrough conduit 64 fromlcollector 53 and classifier 6|, thereby creatinga push on Vent 65 and damper 66 comprise means by which variations inpressure within the system' may be controlled.

In order to prevent leakage of air at the joints, and more particularlyto obtain a clean system,

the vent Ii discharges excess air and moisture, as well as places thesystem as a whole under partial vacuum; The amount of air passagethrough vent '65 is controlled by regulating the damper 66.

Moreover, it the feed is very wet, hot air must be introduced. In suchevent, the damper 66 is opened wider to cause av pronounced suctionthroughout the system, and hot air is then drawn in through conduit froman outside source, the fiow ofthe hot air through conduit 15 beingcontrolled by damper ll.

Even though conduit 15 is on the pressure side of the blower 5|, sincethe whole system is now under a partial vacuum, air will be actuallydrawn in, since the conduit 54 will be at a negative pressure withrespect to theatmosphere.

Thus,there is inthis form of the invention, as in the form of theinvention shown in Fig. 1, means whereby the feed, oversize, and the hotair all mingle together before theyenter the mill 58.

The mill 53 shown in this form of the invention, is of the well-knowntype of conical mill.

Even though the coarse feed is introduced through the discharge end ofsuch form of mill, the coarse feed will migrate to the barrel or centeroi the mill, where the material will be ground by the heavy balls. Thereis a distinct advantage 0! an arrangement of this type over the use of aplain cylindrical mill 0! the'iorm shown in Fig. 1, since the lattertype of mill has no definite way of forcing the coarse material towardsthe far end of the mill. Accordingly, time must be relied upon todistribute the feed throughout the mill II in order to obtain thenecessary grinding results.

Having thus described my invention. what I claim is:

1. A rotary drum mill having a combined feed and discharge opening onlyat one end of the drum and closed at the other end, a blower, an inletconduit leading from said blower to said drum for conducting air intothe drum, a feed conduit for material connected to said inlet conduitexteriorly oi the drum, a classifier, a conduit connecting theclassifier with said drum whereby dust-laden air circulated through thedrum is carried to said classifier, a grate mounted in the drum andspaced from the discharge end of the mill and surrounding but notextending across the inlet conduit whereby the matter discharged fromthe mill to said classifier-drum conduit passes through said grate andthe incoming feed enters the mill unrestrictedly through said inletconduit, and means between the grate and the discharge end of the drumfor removing oversize material caught between said grate and thedischarge end of the drum, said last named means having an end portionentering the feed conduit to discharge oversize into said teed conduit.

2. A rotary drum mill having a combined feed and discharge opening onlyat one end of the drum, a screen mounted within the drum and spaced fromthe discharge end thereof, said screen having a central opening thereinfor the incoming feed, means between the screen and the discharge end ofthe drum for removing oversize material caught between said screen andthe discharge end of the drum, said last named means having an endportion enteringthe central opening to discharge oversize into saidcentral opening.

3. An apparatus or the class described comprising a drum mill containinga plurality of grinding bodies iree to move in all directions therein,said mill being closed at one end and having an opening at the oppositeendya horizontal conduit positioned in said opening for de-' liveringheated air under pressure to the mill, another conduit extending fromsaid opening to an air classifier and adapted to convey the groundproducts suspended in exhaust air to said classifier, a screen mountedwithin the mill and spaced from the discharge end thereof, said screenhaving a central opening therein registering with the first mentionedconduit, means between the screen and the discharge end 01' the mill forremoving oversize material caught between said screen and the dischargeend, said means having an end portion entering the first mentionedconduit to deliver the oversize to said conduit, means to pass the feedin a relatively turbulent condition through the classifier and in suchpronmity to the exhaust air from the mill that fines and dust in thefeed are removed therefrom, and means to convey the dust-free air andclassifier oversize to the heated air conduit where they are dried anddelivered to the mill.

EAR-LOWE HARDINGE. 50

